class Block

class Block extends DisplayPluginBase {
    
    /**
     * Whether the display allows attachments.
     *
     * @var bool
     */
    protected $usesAttachments = TRUE;
    
    /**
     * The entity type manager.
     *
     * @var \Drupal\Core\Entity\EntityTypeManagerInterface
     */
    protected $entityTypeManager;
    
    /**
     * The block manager.
     *
     * @var \Drupal\Core\Block\BlockManagerInterface
     */
    protected $blockManager;
    
    /**
     * Constructs a new Block instance.
     *
     * @param array $configuration
     *   A configuration array containing information about the plugin instance.
     * @param string $plugin_id
     *   The plugin ID for the plugin instance.
     * @param mixed $plugin_definition
     *   The plugin implementation definition.
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     * @param \Drupal\Core\Block\BlockManagerInterface $block_manager
     *   The block manager.
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityTypeManagerInterface $entity_type_manager, BlockManagerInterface $block_manager) {
        parent::__construct($configuration, $plugin_id, $plugin_definition);
        $this->entityTypeManager = $entity_type_manager;
        $this->blockManager = $block_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($configuration, $plugin_id, $plugin_definition, $container->get('entity_type.manager'), $container->get('plugin.manager.block'));
    }
    
    /**
     * {@inheritdoc}
     */
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['block_description'] = [
            'default' => '',
        ];
        $options['block_category'] = [
            'default' => $this->t('Lists (Views)'),
        ];
        $options['block_hide_empty'] = [
            'default' => FALSE,
        ];
        $options['allow'] = [
            'contains' => [
                'items_per_page' => [
                    'default' => 'items_per_page',
                ],
            ],
        ];
        return $options;
    }
    
    /**
     * Returns plugin-specific settings for the block.
     *
     * @param array $settings
     *   The settings of the block.
     *
     * @return array
     *   An array of block-specific settings to override the defaults provided in
     *   \Drupal\views\Plugin\Block\ViewsBlock::defaultConfiguration().
     *
     * @see \Drupal\views\Plugin\Block\ViewsBlock::defaultConfiguration()
     */
    public function blockSettings(array $settings) {
        $settings['items_per_page'] = 'none';
        return $settings;
    }
    
    /**
     * The display block handler returns the structure necessary for a block.
     */
    public function execute() {
        // Prior to this being called, the $view should already be set to this
        // display, and arguments should be set on the view.
        $element = $this->view
            ->render();
        if ($this->outputIsEmpty() && $this->getOption('block_hide_empty') && empty($this->view->style_plugin->definition['even empty'])) {
            return [];
        }
        else {
            return $element;
        }
    }
    
    /**
     * Provide the summary for page options in the views UI.
     *
     * This output is returned as an array.
     */
    public function optionsSummary(&$categories, &$options) {
        parent::optionsSummary($categories, $options);
        $categories['block'] = [
            'title' => $this->t('Block settings'),
            'column' => 'second',
            'build' => [
                '#weight' => -10,
            ],
        ];
        $block_description = strip_tags($this->getOption('block_description'));
        if (empty($block_description)) {
            $block_description = $this->t('None');
        }
        $block_category = $this->getOption('block_category');
        $options['block_description'] = [
            'category' => 'block',
            'title' => $this->t('Block name'),
            'value' => Unicode::truncate($block_description, 24, FALSE, TRUE),
        ];
        $options['block_category'] = [
            'category' => 'block',
            'title' => $this->t('Block category'),
            'value' => Unicode::truncate($block_category, 24, FALSE, TRUE),
        ];
        $filtered_allow = array_filter($this->getOption('allow'));
        $options['allow'] = [
            'category' => 'block',
            'title' => $this->t('Allow settings'),
            'value' => empty($filtered_allow) ? $this->t('None') : $this->t('Items per page'),
        ];
        $options['block_hide_empty'] = [
            'category' => 'other',
            'title' => $this->t('Hide block if the view output is empty'),
            'value' => $this->getOption('block_hide_empty') ? $this->t('Yes') : $this->t('No'),
        ];
    }
    
    /**
     * Provide the default form for setting options.
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        parent::buildOptionsForm($form, $form_state);
        switch ($form_state->get('section')) {
            case 'block_description':
                $form['#title'] .= $this->t('Block admin description');
                $form['block_description'] = [
                    '#type' => 'textfield',
                    '#description' => $this->t('This will appear as the name of this block in administer >> structure >> blocks.'),
                    '#default_value' => $this->getOption('block_description'),
                ];
                break;
            case 'block_category':
                $form['#title'] .= $this->t('Block category');
                $form['block_category'] = [
                    '#type' => 'textfield',
                    '#autocomplete_route_name' => 'block.category_autocomplete',
                    '#description' => $this->t('The category this block will appear under on the <a href=":href">blocks placement page</a>.', [
                        ':href' => Url::fromRoute('block.admin_display')->toString(),
                    ]),
                    '#default_value' => $this->getOption('block_category'),
                ];
                break;
            case 'block_hide_empty':
                $form['#title'] .= $this->t('Block empty settings');
                $form['block_hide_empty'] = [
                    '#title' => $this->t('Hide block if no result/empty text'),
                    '#type' => 'checkbox',
                    '#description' => $this->t('Hide the block if there is no result and no empty text and no header/footer which is shown on empty result'),
                    '#default_value' => $this->getOption('block_hide_empty'),
                ];
                break;
            case 'exposed_form_options':
                $this->view
                    ->initHandlers();
                if (!$this->usesExposed() && parent::usesExposed()) {
                    $form['exposed_form_options']['warning'] = [
                        '#weight' => -10,
                        '#markup' => '<div class="messages messages--warning">' . $this->t('Exposed filters in block displays require "Use AJAX" to be set to work correctly.') . '</div>',
                    ];
                }
                break;
            case 'allow':
                $form['#title'] .= $this->t('Allow settings in the block configuration');
                $options = [
                    'items_per_page' => $this->t('Items per page'),
                ];
                $allow = array_keys(array_filter($this->getOption('allow')));
                $form['allow'] = [
                    '#type' => 'checkboxes',
                    '#default_value' => $allow,
                    '#options' => $options,
                ];
                break;
        }
    }
    
    /**
     * Perform any necessary changes to the form values prior to storage.
     *
     * There is no need for this function to actually store the data.
     */
    public function submitOptionsForm(&$form, FormStateInterface $form_state) {
        parent::submitOptionsForm($form, $form_state);
        $section = $form_state->get('section');
        switch ($section) {
            case 'block_description':
            case 'block_category':
            case 'allow':
            case 'block_hide_empty':
                $this->setOption($section, $form_state->getValue($section));
                break;
        }
    }
    
    /**
     * Adds the configuration form elements specific to this views block plugin.
     *
     * This method allows block instances to override the views items_per_page.
     *
     * @param \Drupal\views\Plugin\Block\ViewsBlock $block
     *   The ViewsBlock plugin.
     * @param array $form
     *   The form definition array for the block configuration form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     *
     * @return array
     *   The renderable form array representing the entire configuration form.
     *
     * @see \Drupal\views\Plugin\Block\ViewsBlock::blockForm()
     */
    public function blockForm(ViewsBlock $block, array &$form, FormStateInterface $form_state) {
        $allow_settings = array_filter($this->getOption('allow'));
        $block_configuration = $block->getConfiguration();
        foreach ($allow_settings as $type => $enabled) {
            if (empty($enabled)) {
                continue;
            }
            switch ($type) {
                case 'items_per_page':
                    $form['override']['items_per_page'] = [
                        '#type' => 'select',
                        '#title' => $this->t('Items per block'),
                        '#options' => [
                            'none' => $this->t('@count (default setting)', [
                                '@count' => $this->getPlugin('pager')
                                    ->getItemsPerPage(),
                            ]),
                            1 => 1,
                            2 => 2,
                            3 => 3,
                            4 => 4,
                            5 => 5,
                            6 => 6,
                            10 => 10,
                            12 => 12,
                            20 => 20,
                            24 => 24,
                            40 => 40,
                            48 => 48,
                        ],
                        '#default_value' => $block_configuration['items_per_page'],
                    ];
                    break;
            }
        }
        return $form;
    }
    
    /**
     * Handles form validation for the views block configuration form.
     *
     * @param \Drupal\views\Plugin\Block\ViewsBlock $block
     *   The ViewsBlock plugin.
     * @param array $form
     *   The form definition array for the block configuration form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     *
     * @see \Drupal\views\Plugin\Block\ViewsBlock::blockValidate()
     */
    public function blockValidate(ViewsBlock $block, array $form, FormStateInterface $form_state) {
    }
    
    /**
     * Handles form submission for the views block configuration form.
     *
     * @param \Drupal\views\Plugin\Block\ViewsBlock $block
     *   The ViewsBlock plugin.
     * @param array $form
     *   The form definition array for the full block configuration form.
     * @param \Drupal\Core\Form\FormStateInterface $form_state
     *   The current state of the form.
     *
     * @see \Drupal\views\Plugin\Block\ViewsBlock::blockSubmit()
     */
    public function blockSubmit(ViewsBlock $block, $form, FormStateInterface $form_state) {
        if ($items_per_page = $form_state->getValue([
            'override',
            'items_per_page',
        ])) {
            $block->setConfigurationValue('items_per_page', $items_per_page);
        }
        $form_state->unsetValue([
            'override',
            'items_per_page',
        ]);
    }
    
    /**
     * Allows to change the display settings right before executing the block.
     *
     * @param \Drupal\views\Plugin\Block\ViewsBlock $block
     *   The block plugin for views displays.
     */
    public function preBlockBuild(ViewsBlock $block) {
        $config = $block->getConfiguration();
        if ($config['items_per_page'] !== 'none') {
            $this->view
                ->setItemsPerPage($config['items_per_page']);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function usesExposedFormInBlock() {
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function remove() {
        parent::remove();
        if ($this->entityTypeManager
            ->hasDefinition('block')) {
            $plugin_id = 'views_block:' . $this->view->storage
                ->id() . '-' . $this->display['id'];
            foreach ($this->entityTypeManager
                ->getStorage('block')
                ->loadByProperties([
                'plugin' => $plugin_id,
            ]) as $block) {
                $block->delete();
            }
        }
        if ($this->blockManager instanceof CachedDiscoveryInterface) {
            $this->blockManager
                ->clearCachedDefinitions();
        }
    }

}